FIG. 1 of the drawings attached hereto shows the entire construction of a part whereby a cab is mounted on a dump truck. A dump truck 1 has a frame 2 to which are fastened a pair of brackets 3 and 4 for supporting a floor 6 of a cab 5 via a pair of liquid sealed suspension units 10 and 10. A said liquid sealed suspension unit 10 is effective to prevent vibrations from a road and so forth from being transmitted directly to the said cab 5.
FIG. 2 is a detailed view of a portion .PI. of FIG. 1. To the said bracket 4 there is fastened a casing 11 of the said liquid sealed suspension unit 10 by means of a bolt 12 and a nut 13. The said liquid sealed suspension unit 10 has a guide shaft 14 that is fastened to the said floor 6 by means of a nut (or bolt) 15. Thus, the said cab 5 in a state in which vibrations may be absorbed by means of the said liquid sealed suspension 10 is mounted on the said bracket 4.
As a said liquid sealed suspension unit 10 of this sort which effectuates a vibration absorption requirement there have hitherto be known what are shown in FIGS. 3 and 4.
In what is shown in FIG. 3, the said guide shaft 14 having a bolt 16 is coupled to the said casing 11 via a cylindrical rubber mount 17. The said casing 11 has one end fastened to a vessel 20, that is formed therein with a liquid sealed chamber 29 in which a damping liquid 21 is sealed. The said liquid sealed chamber 29 contains a damper plate member 23 with a rubber stopper 24, which is fastened to the downward end of the said guide shaft 14 by means of a bolt 22. The said damper plate member 23 is formed with a bore 25 whereas the said vessel 20 is formed with an inlet port 26.
The said damping liquid 21 is injected or poured into the said liquid sealed chamber 29 through the inlet port 26 of the said vessel 20, and the bore 25 in the said damper plate member 23 is used to inject or pour the said damping liquid 21 into an upper cavity of the said damper plate member 23.
And, if a vertical (axial) vibratory load is applied to the said guide shaft 14, the said damper plate member 23 acts to agitate the damping liquid 21 so that the vibrations may be damped with a damping force that is then generated.
Also, in what is shown in FIG. 4, a casing 30 is coupled with a guide shaft 31 having a bolt 16 via a cylindrical rubber mount 33 that consists of cylindrical rubber sections of an identical thickness laminated with intervening cylindrical plate members 32. The said guide shaft 31 has a whirl-stop pin 34 that is effective, when the said bolt 16 is fastened, to prevent the said guide shaft 31 itself from being turned. A downward end of the said casing 30 and a stopper plate 36 has fastened thereto a vessel 35 in which a said liquid sealed chamber 29 containing a said damping liquid 21 is formed. The said liquid sealed chamber 29 also contains a said damper plate member 23 fastened to the downward end of the said guide shaft 31 by means of a said bolt 22 as well as the said stopper plate 36. The said damper plate member 23 has a rubber stopper 37 fastened to its upper surface and a foamed elastic body 38 securely sandwiched between its lower surface and a plate 39.
Of the above mentioned constructions which have been adopted in the prior art, what is shown in FIG. 3 has the problem that the said damper plate 23, due to its circular configuration, has only been effective to generate a damping force in its axial direction. However, the said rubber mount 17 which is designed to produce a vibration absorbing action both in its axial and transverse directions has, due to its transverse rubber stiffness that is lower than its vertical rubber stiffness because of its unitary structure with a large thickness, allows vibrations with a complicated orientation to be set free in the transverse direction, and hence a cause to generate a rolling from side to side.
On the other hand, what is shown in FIG. 4 and has been adopted also in the prior art is characterized by a construction in which the said rubber mount 33, due to its laminated structure, has had its transverse spring constant that is higher than that in what is shown in FIG. 3 and its axial spring constant that is reasonably high as well. However, with such a construction, the displacement component attainable in the axial direction, rather than the radial rubber distortion constant related to the rubber durability, remains within the order of .+-.6 mm and cannot be largely taken. Therefore, this has the problem that a vehicle therewith is not comfortable to ride in and its vibration absorptivity is thus poor in spite of the fact that there may not be a roll due to a transverse vibratory component since the transverse spring constant is large (stiffness is high) because of a laminated structure of rubber sections which are of an identical thickness.
The present invention has taken account of the above mentioned problems in the prior art and has for its object to provide a liquid sealed suspension unit whereby a vehicle therewith becomes comfortable to ride in owing to the fact that an increased vibratory amplitude can be taken in the axial direction and the rubber durability that is related to the said increased vibratory amplitude and hence the damping effect can be markedly enhanced, and an excellent vibration absorbing effect as a whole can be obtained owing to the fact that there can be no roll due to vibrations in complicated directions because of both the transverse damping action and the small amplitude vibration absorbing action which can be enhanced.